Blurring the lines between aggregate and binder

Concrete producers have known for a long time that optimizing the particle size distribution of concrete aggregates allows for a higher strength concrete. Optimizing the particle size distribution reduces the amount of free space around the aggregate particles and thus requires less binder paste. Most concrete producers use sand as a fine aggregate. Sand can be as fine as 100 microns in size, but is often in the 1000 micron range. The fineness of available sand typically determines the fine end of the aggregate particle packing distribution for concrete production.

Today cement binders are often composed of different combinations of pure Portland cement and supplemental cementitious materials. These binders are composed of particles mostly below 45 microns in size. Large binder particles take more time to react and particles above 45 microns in size may never completely react. Work in concrete mix optimization indicates that concrete can be produced more economically when the principles of particle packing density are continued down through the binder size range.

Research has shown that substituting the larger binder particles for less reactive or inert fillers can produce concrete with similar strength but with a lower cost and environmental footprint.

Author: J. Guynn, J. Kline

Section: Concrete

Keywords: aggregate, concrete, Portland cement, particle packing density, void volume, supplemental cementitious materials